In the field of magnetic recording typically used for hard discs, recording density of 200 Gbit/inch2 or higher in areal density has been achieved thanks to the improvement in characteristics of recording media, recording heads, and reproducing heads, and the density is improving even more. In response to this improvement in recording density, various magnetic recording methods and magnetic reproduction methods have been proposed.
As one of magnetic recording methods adopted in current models of hard discs, a photo-assist reproduction method has been proposed with the view to reading out, in high resolution, magnetically-recorded information which is recorded on a magnetic recording medium at high density. This reproduction method is arranged in such a way that laser light is applied to a magnetic recording medium which records magnetically-recorded information thereon so that the magnetic recording medium is locally heated to a temperature lower than the temperature in the recording, and a leakage magnetic field generated from the heated area is detected by using a magnetic sensor. In adopting this method, the material and composition of the recording medium are adjusted in advance so that a non-heated area of the magnetic recording medium rarely generates a leakage magnetic field whereas a heated area of the magnetic recording medium generates an intense leakage magnetic field. This allows the magnetic sensor to detect a relatively strong leakage magnetic field from the heated area, thereby making it possible to restrain crosstalk from neighboring tracks. In this photo-assisted reproduction, an area from which information is reproduced (i.e. an area generating an intense leakage magnetic field) is determined in accordance with the size of a heated area on the recording medium. It is therefore possible to reproduce information in high resolution from microscopic recording bits, when the size of the heated area is reduced by adopting a near field light source as the heat source.
An example of the aforesaid scheme adopting a near field light source and a magnetic sensor is a below-described patent document 1. This patent document 1 discloses a photo-assisted magnetic head including: a coil which applies a magnetic field to around a laser light emission opening so that information is recorded; and a magnetic sensor which is placed inside the coil and detects information recorded on a magnetic recording medium. This document also discloses a photo-assisted magnetic head including either a plasmon exciting member which enhances laser light emitted from the laser light emission opening or a light-blocking member which is capable of reducing the size of the opening. The patent document 1 also teaches that the invention makes it possible to shorten the distance between the laser light emission opening and a spin valve film of a magneto-resistive device used in the magnetic sensor to be 2-3 μm and hence adjustments during construction become easy, thereby allowing the laser light emission opening and the magnetic sensor to simultaneously track a single narrow track.    [Patent Document 1] Japanese Unexamined Patent Publication No. 2003-203304